As will be well-known, a comb filter used in a television receiver and the like is to separate a video signal (television signal) on a frequency axis. Since such prior art separation filter on the frequency axes is not generally applicable, it performs a calculation process in such a manner that a mean value in all areas on a picture screen becomes an optimum value thus resulting in a remarkable error in a local part such as an edge of the picture.
By way of example, if the video signal for television is processed by the aforesaid comb filter, a dot interference and the like are likely to occur.